CH 104 Seminar Practice Problems Answer Key

COMPLETE ALL PRACTICE PROBLEMS BEFORE THE SEMINAR CLASS

Practice problems for CH 104 seminar, week #1

 

1. Classify as chemical (C) or physical (P):

 

a) color i) exists as a solid at room temperature

b) odor j) a waxy solid dissolves in gasoline

c) melting point k) a shiny solid turns black upon heating in air

d) boiling point l) a colorless liquid produces a gas when treated with electricity

e) combustible m) a snowball disappears in a freezer after several days

f) magnetic n) sand is separated from water by filtration

g) salt dissolves in water o) gasoline is removed from crude oil by distillation

h) an abandoned car rusts p) a stick of dynamite explodes

 

a) P b) P c) P d) P e) C f) P g) P h) C i) P j) P k) C l) C

m) P n) P o) P p) C

 

2. Classify as a mixture or a pure substance:

a) oxygen b) 100% pure apple juice c) water

d) NH3 e) household ammonia solution f) unpolluted air

 

a) PS b) M c) PS d) PS e) M f) M

 

3. Classify as an element or a compound:

a) oxygen b) water c) N2

d) CO e) Co f) CoCl3

 

a) E b) C c) E d) C e) E f) C

 

4. Indicate the number of significant figures in each measurement given below in (a)

and (b); complete the two calculations to the correct number of significant figures

and correct units.

 

__5__ s.f.

(a) 2.1250 g = 0.044 g/cm3

(12.000 cm)(2,002 cm)(0.0020 cm)

__5__ s.f. __4__ s.f. __2__ s.f.

 

 

(b) 1.200 g + 725.10 g + 1,125.000 g = 1851.30 g

__4_ s.f. __5_ s.f. __7_ s.f.

 

 

5. Write your answers in 4(a) and 4(b) in scientific notation.

 

(a) 4.4 x 10-2 g/cm3 (b) 1.85130 x 103 g

 

 

6. In each of the following, solve for Q using the correct number of significant digits.

 

a) 450.0 x Q = 3.00 b) Q = 1.703 c) Q 0.111 = 9.25

5.1256

 

Q = 3.00 / 450.0 Q = (1.703) (5.1256) Q = 9.25 + 0.111

 

Q = 0.00667 (3 sf) Q = 8.729 (4 sf) Q = 9.36 (3 sf)

or 6.67 x 10-3